A pressure increasing system is a device configured to increase a pressure of a target gas to a target pressure.
In recent years, problems such as global warming due to increases in emission of carbon dioxide, which is known as a greenhouse gas, has become significant. In particular, a technique in which, when a large amount of carbon dioxide is contained in exhaust gases from thermal power plants, the carbon dioxide is separated out and collected, a pressure increasing system then increases a pressure, the gas is stored in the ground or the seabed, and carbon dioxide in the atmosphere is reduced is known.
More specifically, in the pressure increasing system, carbon dioxide is repeatedly compressed and cooled by compressors and an intercooler which are provided in multiple stages, and carbon dioxide with a critical pressure or higher and a critical temperature or higher is then additionally cooled. Therefore, carbon dioxide with a temperature and pressure optimal for transport and storage is obtained.
Here, in the pressure increasing system disclosed in Patent Literature 1, some of the carbon dioxide (intermediate supercritical pressure liquid) with a critical pressure or higher is extracted in a portion before a pump portion, is depressurized to about the critical pressure and is used as a refrigerant for cooling the carbon dioxide itself. In the pressure increasing system disclosed in Patent Literature 1, when the same gas is used as the refrigerant, it is furthermore possible to cool the carbon dioxide to about the critical temperature at which it is suitable to increase a pressure in the pump portion in contrast to when carbon dioxide is cooled using only a general cooler (a shell and tube type heat exchanger). Therefore, it is possible to reduce the power (head) required for increasing the pressure.